Islamic State has released a new message purportedly from its reclusive leader, saying his self-styled "caliphate" is "doing well” and that airstrikes by Russia and a U.S.-led coalition have failed to weaken the group.

“Be confident that God will grant victory to those who worship him, and hear the good news that our state is doing well. The more intense the war against it, the purer it becomes and the tougher it gets,” said the audio recording, described as having been made by Abu Bakr al-Baghdadi.

The authenticity of the 24-minute message, posted Saturday on Twitter accounts that have published Islamic State statements in the past, could not be verified.

The message criticized Saudi Arabia's efforts to set up a coalition of Muslim nations to fight IS. “If it was an Islamic coalition, it would have declared itself free from its Jewish and Crusader lords and made the killing of the Jews and the liberation of Palestine its goal,” the message said.

The French news agency AFP reported that the speaker also called for an uprising in Saudi Arabia and pledged to attack Israel.

He called on Saudi citizens to “rise up against the apostate tyrants, and avenge your people in Syria, Iraq and Yemen.”

Baghdadi regularly attacks the Saudi kingdom verbally in his recordings. In his last message, Baghdadi accused Saudi rulers of launching an air campaign against Shi'ite Houthi rebels in Yemen only to please the West.

In the latest recording, the speaker pledged to attack Israel, saying IS has “not forgotten Palestine for a single moment.”

“And soon, soon with God's permission, you will hear the footsteps of the mujahedeen. We are getting closer to you day by day,” he said.

AFP said the recording did not appear to be accompanied by multilingual transcripts, which has been the case with other Baghdadi audio messages.

The militant Sunni Islamist group controls swaths of Iraq and Syria but has come under intensifying military pressure in recent weeks.

An alliance of Syrian Kurds and Arab rebel groups, backed by U.S. coalition planes, said it captured a Syrian dam on Saturday from Islamic State, cutting a main supply route of the militants across the Euphrates.

In Iraq, government troops were pushing deeper into the heart of the last remaining district held by Islamic State in the city of Ramadi.

The last online public message said to have come from Baghdadi was posted in May. He has been reported injured or killed several times in fighting, apparently incorrectly.